1. Field of the Invention
The present invention relates generally to fuel quantity indicators for vehicles, and more particularly to systems and methods for checking the fuel quantity of a vehicle based on vehicle performance.
2. Description of the Related Art
In the event of an aircraft being dispatched without operational fuel quantity indicators, the aircraft's total fuel quantity is calculated via the “known” amount of fuel in the tanks at the beginning of the flight (calculated by ground personnel and confirmed by the flight crew) and then decremented by onboard computers (such as the flight management system (FMS)) as fuel is burned in-flight. Although this system is typically very accurate, it is fully dependent upon being correctly initialized with the proper information.
A well-known example of improper initialization is illustrated by the case of the “Gimli Glider,” the nickname of an Air Canada aircraft that was involved in an unusual aviation incident in 1983. In Air Canada flight 143, the state-of-the-art Boeing 767 aircraft ran out of fuel while at cruise due to a clerical error in kg/lb unit conversions, resulting in the aircraft only being filled with less than half the required amount of fuel needed for the flight. The aircraft was supposed to take 22,300 kg of fuel. However, it was filled with 22,300 lbs instead (less than half of the required amount). Due to this particular aircraft's fuel quantity indicators being inoperable, there was no indication of this fuel shortage. Since the FMS had been programmed with the assumed (yet incorrect) quantity that the aircraft should have been filled with, everything appeared normal to the crew with no indication that the aircraft was flying with almost 27,000 pounds of fuel absent. Performance characteristics depend significantly on the gross weight (and center of gravity) of the aircraft. In the example Air Canada incident, the aircraft would have taken off with approximately a 7-10% lighter gross weight than intended, with a displaced center of gravity. This would have resulted in significant takeoff and climb performance deltas from those expected, in addition to different trim settings needed for cruise.
There has been a partial response to this problem. U.S. Pat. No. 8,467,918 B2, issued to Lieu entitled, “HEURISTIC METHOD FOR COMPUTING PERFORMANCE OF AN AIRCRAFT,” discloses a method for estimating the vertical airspeed and fuel flow of an aircraft at a point along a flight plan using other aircraft parameters for that point. The process uses a database having entries containing sets of actual values of operating parameters obtained during prior aircraft flights. The database is sorted by data set aggregate values that are is calculated from each set of actual values. When the vertical airspeed and fuel flow estimates are needed, a section thereof is identified based on the aggregate values. That section of the database is analyzed to identify the set of actual operating parameters values that best matches the other aircraft parameters for the flight plan point. The vertical airspeed and fuel flow values from that identified set are used as the estimates. The process reduces the amount of the database that has to be analyzed to locate the data to use.
U.S. Pat. No. 4,837,695, issued to Baldwin, entitled, “METHOD AND APPARATUS FOR PREDICTING AND MONITORING AIRCRAFT TAKEOFF PERFORMANCE,” discloses a method for predicting and monitoring the takeoff performance of an aircraft uses information from one or more previous takeoffs of the aircraft to generate a prediction of the takeoff performance for the current takeoff. In the preferred embodiment, a takeoff profile for the current takeoff is generated and includes information about predetermined characteristics of the aircraft and information about ambient conditions at an airport from which the takeoff is being monitored. Expected performance data for the current takeoff is then generated from the takeoff profile and used to select a set of actual performance data previously stored from the one or more previous takeoffs. A selected “best fit” actual performance data set is then displayed in an appropriate fashion. Upon takeoff, a set of monitored performance data is generated as a function of one or more of sensed takeoff parameters. The monitored performance data set for the current takeoff is then displayed in conjunction with the actual performance data previously selected to provide the crew with an indication of the progress of the current takeoff.
Both of the above patents disclose methods for observing and predicting the performance of an aircraft; however, neither method uses the observed performance as a means of checking for an error in the data used to make the prediction. An error that is particularly of interest is a discrepancy in fuel quantity, and this will be the focus of the method as described herein.